Texas Wastewater Class B Practice Exam

What condition might an operator suspect when observing boiling action in an aeration tank?

1. Low dissolved oxygen levels

2. Improper sludge age

3. Over aeration resulting in high dissolved oxygen

4. Insufficient mixing of sludge

The correct answer is: Over aeration resulting in high dissolved oxygen

The presence of boiling action in an aeration tank typically indicates that there is over aeration, which results in high levels of dissolved oxygen. When air is introduced into an aeration tank, it is intended to provide oxygen to microorganisms that break down organic matter in the wastewater. However, if too much air is introduced, the dissolved oxygen levels can exceed what is necessary for the biological processes, leading to excessive bubbling or boiling action. This phenomenon can disrupt the treatment process and negatively affect the microorganisms that rely on a balanced level of oxygen. In contrast, low dissolved oxygen levels could lead to insufficient aeration, which would not produce boiling action. Improper sludge age relates to the time microorganisms have been in the treatment process, while insufficient mixing of sludge might lead to dead zones in the tank but wouldn't typically cause boiling behavior. Thus, the observation of boiling action strongly correlates with over aeration, making the association with high dissolved oxygen levels accurate.